Version 7 production and 9 development. In fact believe standard
install of "leaves" has "Sick Leaves" already setup.

So when you allocate a user "legal leave" their holiday say 20 days.
Then they just book in their time under that for holiday. For sick
they use "sick leaves", which goes to minus figures... unless the
company has a policy of maximum paid sick. Then you could create an
allocation for that sick and report if it goes under 0.